FIG. 5 shows a schematic side view of a conventionally known cylindrical linear motor, and FIG. 6 is a side cross-sectional view thereof. A cylindrical linear motor according to the present invention includes, as shown in FIG. 5, a stator having a field pole 10, and a mover having an armature 20 coaxially arranged around the field pole 10. The present invention relates to improvements of the field pole 10 and the armature 20.
The field pole 10 includes, as shown in FIG. 6, a plurality of cylindrical columnar magnets 10a each magnetized in the axial direction, cylindrical columnar pole pieces 10b made of a magnetic material each disposed between adjacent magnets 10a, a stainless steel pipe 10c housing the magnets 10a and the pole pieces 10b therein, and end blocks 10d provided at both axial ends of the stainless steel pile 10c. The magnets 10a are arranged so that the magnetic direction changes alternatively. In other words, the adjacent magnets are arranged so that the same magnetic poles N or S face each other. The end blocks 10d are attached to both end portions of the stainless steel pipe 10c to bear against the repulsion force generated between the magnets.
On the other hand, the armature 20 includes, as shown in FIG. 6, cylindrical coils 20a, a cylindrical yoke 20b made of a magnetic material, and an aluminum frame 20d. That is, a plurality of cylindrical coils 20a are arranged in the axial direction and disposed inside of the cylindrical yoke 20b, and the aluminum frame 20d is provided outside of the cylindrical yoke 20b. The frame 20d is made of aluminum to secure the mechanical rigidity of the armature 20 and reduce the weight of the armature 20.
The field pole 10 and the armature 20 are disposed coaxially via a magnetic gap to thereby constitute a linear motor in which the field pole 10, as a stator 1, and the armature 20, as a mover, can move relatively.
The use of the cylindrical yoke 20b increases the gap magnetic flux density, resulting in a high-performance motor. Furthermore, inducing the flux generated from the field pole 10 into the cylindrical yoke 20b reduces the flux leakage to the aluminum frame 20d, which in turn can restrain the viscous braking force.
As to the end block 10d tightly fixed to the end portion of the stainless steel pipe 10c which accommodates a plurality of magnets 10a with the same magnetic poles facing with each other, such end block is disclosed in, for example, Patent Document 1. FIG. 7 is a cross-sectional view showing a stator 1 for explaining an end block.
In FIG. 7, “70” denotes a field pole, “70a” denotes each of a plurality of magnets arranged with the same magnetic poles facing with each other, “70c” denotes a pipe made of a non-magnetic material for covering the outer periphery of the magnets, “70e” denotes a shaft made of a non-magnetic material with threaded end portions, the shaft penetrating all of the magnets 70a, and “70d” denotes an end block into which the threaded portion of the shaft 70e is screwed. It is constituted such that a driving force is generated in the axial direction of the stator by the leakage flux generated from the magnets 70a and the energized coils in the mover 10. The fastening of the stator is performed by tightening the end block 70d to the threaded portion 70f of the shaft 70e. 